Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
1998-12-11
2001-05-15
Cooney, Jr., John M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S079000, C521S085000, C521S092000, C521S093000, C521S094000, C521S146000, C521S149000
Reexamination Certificate
active
06232357
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to compositions based on elastomeric polymers of vinylidene fluoride, hexafluoropropene and, optionally, tetrafluoroethylene.
The above-identified polymers are being used more and more in fields where high chemical stability and exceptional resistance to temperatures exceeding 220° C. for continuous use are required. Because of these characteristics, these fluoroelastomers are used particularly for producing gaskets, O-rings, and seals of high technological value.
DESCRIPTION OF THE PRIOR ART
Because of the intrinsic characteristics of their chemical structure, the specific density of these fluoroelastomers varies from 1.78 to 2.01. This results, of course, in final articles comprising the compound having high specific densities. The cost of the articles is affected by this property. This, in turn, has retarded the use of these fluoroelastomers in fields is where the excessive weight of the final article has led to an unacceptable difference in cost which favors other rubbers having lesser chemico-physical properties.
The production of non-fluorinated elastomeric articles having a lower final weight through the use of formulations capable of providing microcellular foamed products is a generally known technology, applicable on an industrial scale
This technology—utilized, for example, for natural and silicone rubbers—comprises the use of blends which, besides the usual curing systems, contain appropriate foaming agents. These foaming agents, as a consequence of their thermal decomposition during the processing step, are capable of generating gases, mainly nitrogen and carbon oxides, which swell the elastomeric material.
The main classes of such swelling agents are:
azodicarbonamide and its derivatives;
variously substituted hydrazides, for example p.toluene sulphonyl hydrazide.
In order to control their thermal decomposition to meet processing requirements, such swelling agents can be associated with appropriate kickers, which modify the thermal decomposition kinetics thereof.
Examples of such kickers are:
organic acids (for example salicylic, glycolic, lactic, citric, succinic acids);
phosphoric acid;
organic bases (for example guanidines and ethanolamines);
inorganic bases (for example borax and potassium carbonate);
zinc, mercury, barium, cadmium, calcium, strontium, magnesium, lead, tin, silicium compounds.
In the case of the above-described vinylidene fluoride elastomeric polymers, the use of this technology has not yet permitted the production of foamed articles having acceptable appearance and physico-mechanical characteristics. In the best of circumstances, spongy materials with large bubbles and large inner cavities and a wrinkly surface appearance have been obtained.
SUMMARY OF THE INVENTION
It has now been found that the use of particular combinations of components usually used for the curing of the above-described fluoroelastomers, and of particular components known as swelling agents—each of these components being used in well-defined proportions—permits the production of microcellular foamed articles endowed with excellent characteristics as regards the dimensional and cell distribution homogeneity, the outer appearance, and their physico-mechanical properties.
Thus, it is an object of the present invention to provide compositions based on elastomeric polymers of vinylidene fluoride, hexafluoropropene and optionally tetrafluoroethylene suitable for providing microcellular foamed vulcanized articles exhibiting the above-described characteristics.
REFERENCES:
patent: 3868337 (1975-02-01), Gros
patent: 4259463 (1981-03-01), Moggi et al.
patent: 5883197 (1999-03-01), Barbieri et al.
Barbieri Franco
Ferro Raffaele
Fiorillo Giuseppe
Ausimont S.p.A.
Bryan Cave LLP
Cooney Jr. John M.
Stiefel Maurice B.
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